07 Apr Autumnal Propagation in Southern Australia
Last Updated on April 7, 2021
If you’re interested in tropospheric propagation, Autumn in the southern states of Australia is one of the best times to get on the bands. April is the time when the atmosphere is stable. It’s the time of large high-pressure systems that cross the Great Australian Bight. They deliver still, clear and sunny days along with cold and still nights – the perfect environment for an inversion.
Mount Martha is on the Mornington Peninsula, just on 70km south of Melbourne. My station is 70 metres above sea level with unencumbered views from Port Phillip heads to the south to the North Eastern suburbs of Melbourne.
Propagation to the west is very reliable and at this time of year and it’s not uncommon to work coastal troppo into the South Australian town of Mt Gambier on a daily basis. The path from Mt Gambier to Mt Martha is relatively flat.
I use a dual-band 2 and 70 cm Yagi as well as an 18 element 23cm antenna both made by Antennas Amplifiers. These antennas work exceptionally well as well as providing a home for the local spiders.
April is known for large high-pressure weather systems that bring stable weather to the southeast coast of Australia. High-pressure systems are known as anticyclonic systems and these systems are responsible for subsidence temperature inversions. Temperature inversions usually form at dawn and dusk – the best time of day for DX.
Ducts tend to develop progressively through the lifetime of an anticyclone, so the biggest tropo openings tend to occur after several days of enhanced propagation. In Autumn, we tend to get the best of both SUBSIDENCE and RADIATION inversion mechanisms. Traffic on 2m in VK3 tends to peak during the Autumn months, especially over the Easter break.
The VK7RAE beacon is located on the northern beaches of Tasmania near Devonport. From Mt Martha, I don’t have a direct path to VK7 as Arthurs Seat and Red Hill provide a 300m obstacle that just blocks RF in its tracks, so to overcome the problem, I go around it. If you can’t work a station directly, try bouncing off a nearby obstacle.
Working troppo is a lot of fun, especially when there are plenty of stations to work. You don’t need to be a home station with the latest gear either. Mobile and portable stations can have troppo contacts just as easily as home stations. So get on the radio at dawn and dusk and call CQ. You never know who may answer.